Question: I know this would be an extremely rare instance but, what would happen if East is lucky enough to have a winning hand after the Charleston?

Answer: If East is lucky enough to have a winning hand after the Charleston, the hand is considered self-picked and the value of that hand is doubled.  This is also referred to as an “Earthly Hand” If the 5th player bet on East, they are paid just like the winner. Also see ID94)

Source:   Mah Jongg Made Easy 2020 page 14 Bullet 7 and page 27, Five-Handed Mah Jongg